The present invention relates to methods and apparatuses for producing visual and other surface effects in a finished thermoplastic product by directly applying at least one color-containing thermoplastic resin system to at least one surface of an extruded thermoplastic substrate. The present invention also relates to the finished articles.
In the thermoplastic molding industry, the color and surface aesthetics of the final molded product dramatically influences the end user""s view of that product and, in turn, these ultimately dictate how well it will sell. The ability to provide unique or enhanced colors or other surface aesthetics can dramatically increase both the variety of applications for which such a thermoplastic will be accepted and also allows the molded product to be distinguished from its competition.
Some of the more desirable conventional visual effects are typically known as graining, mottling, blotching, marbling, streaking and variegation. One highly desirable aesthetic appearance for thermoplastic sheet materials is that of natural granite. This particular visual effect has been generally referred to in the art as either xe2x80x9cgranite-lookxe2x80x9d or xe2x80x9cgranite-like.xe2x80x9d
Granite-look and other surface effects have typically been generated in the thermoplastic art by incorporating some form of additive into the thermoplastic resin system prior to molding or extrusion. Such methods exhibit several significant drawbacks.
While granite-look articles have been extremely desirable, previous methods for preparation of granite-look thermoplastic products have typically employed large diameter pigments or large agglomerations of smaller pigments within the molded resin itself. The loaded resin is then processed in such a manner that these pigments or pigment agglomerates are visible. Because most commercially-available pigments are of very small size, preparation of large particle sizes or agglomerates is difficult and expensive. Further, controlling particle size during currently used methods for manufacture, specifically, compounding by extrusion or casting, is problematic.
It will also be appreciated by the skilled artisan that virtually any additive that is placed in a thermoplastic resin system primarily to generate an aesthetic effect will compromise the physical properties of the finished product. Particularly, when dealing with opaque thermoplastics, both the nature and quantity of materials employed in the art to produce these aesthetic effects have caused significant decreases in important physical properties, such as impact strength and weatherability. Further, the nature and quantity of the materials previously employed in the art (once again, especially in opaque thermoplastics) have also created some significant processing problems; when sufficient amounts of certain additives are employed in order to generate a granite-like appearance in a conventional opaque thermoplastic resin system, these same materials create flow instabilities that can dramatically narrow or shift the process window.
One current method of producing granite-look engineering thermoplastics is to load the thermoplastic resin with a high temperature material such as a thermoset. While loading a thermoplastic resin with a high temperature material can produce desirable visual effects, the loading level that is needed to provide the desired surface effect results in both adverse changes to the process window and also a final product that is far too brittle for most applications.
Another art-disclosed example of producing granite-look engineering thermoplastics employs an additive mixture containing: chopped nylon (or polyester fibers) of the desired colors; titanium dioxide; and a metallic soap dispersant. (See U.S. Pat. No. 5,407,988, issued Apr. 18, 1996 to Gary J. Kogowski, incorporated herein by reference.) This mixture is admixed with a thermoplastic resin system prior to extrusion or injection molding. The fibers coalesce during processing to form specks within the thermoplastic matrix and generate an improved granite-like appearance. Further, in employing this system, no fibers are typically detected in the finished product after extrusion or injected molding. However, there is a limitation on the amount of such an additive mixture that can be employed without the processing window being narrowed and/or an associated reduction in important physical properties.
Because employing such additives in injection or extrusion molding resin systems have such a negative impact on both processing and physical properties, the art has also employed casting-type molding. While casting addresses some of the processing concerns discussed above, it does not eliminate them all together. Other art-disclosed ways of generating such surface aesthetics on thermoplastics include, for example, molding-in surface texture (alone or in combination with incorporating additives to the base resin prior to molding as discussed above). Another method involves flexo or gravure printing of the desired image or aesthetic on a thin film and then laminating the thin film to the sheet thermoplastic material. While printing and photographing such patterns result in accurate reproductions of the desired effect, this process suffers from the significant drawback of having the overall physical properties of the printed film typically being the controlling factor in the scope of applications. Further, the width of films that can be effectively used as a substrate for such methods is limited.
The present invention overcomes many of these disadvantages by directly applying at least one compatible color-containing thermoplastic resin system to at least one surface of a thermoplastic after molding or extrusion, thus achieving a visual effect, such as a granite-look, while avoiding or minimizing any adverse effects on the physical properties or processing of the thermoplastic typically associated with art-disclosed methods.
It is an object of the present invention to simply and efficiently produce a granite-like or other surface effect on an extruded thermoplastic sheet product by directly applying a compatible color-containing thermoplastic resin system to at least one visible surface of the extruded thermoplastic sheet. A compressive force is then applied to the treated surface. Especially useful resin systems for use as the treated substrate in the present invention include styrenic copolymers such as acrylonitrile-styrene-acrylate and acrylonitrile-butadiene-styrene. The methods of the present invention achieve highly desirable visual effects, particularly a granite-like appearance, while minimizing any adverse effects on processing or physical properties, especially impact strength. The desired surface effect is achieved by the interaction of the color-containing thermoplastic resin system and the extruded thermoplastic sheet, without the necessity of using an embossing mechanism, as is common to prior art surface effect thermoplastics which rely on a difference in the concentration of pigment between embossed and non-embossed areas to achieve the desired effect.
It is another object of the present invention to provide both an apparatus for carrying out such methods and the articles produced thereby.